1. Field of the Invention
The present invention relates to a method of accurately and reliably estimating irregular wear of pneumatic tires for vehicles, which occurs on the tread surface of tires during a running period until a rolling distance of about 10,000 km is reached.
2. Description of Related Art
An irregular wear that occurs on the tire tread surface exerts a considerable influence and often degrades various kinds of property and performance of the tire. Accordingly, it is highly desirable to accurately and reliably estimate the manner in which irregular wear occurs on existing tires and prototype tires, respectively. This is because the estimation can be reflected to the design, refinement, etc., of the tread pattern so as to improve the durability of tires and achieve the desired maneuverability for a longer use period.
In this context, there have been various proposals regarding the method of estimating the manner in which irregular wear occurs on the tread surface. For example, JP-A-8-29296 discloses a method of estimating the wearing state of tires, which has been developed by the assignee of this application.
According to the wearing state estimating method disclosed in JP-A-8-29296, a paint is coated on a tread surface of a tire in a regular lattice- or dot-manner, in which the paint is distinct in brightness from the tread surface, and can be deformed following the deformation of the tread surface. The manner in which the wear occurs is estimated based on the wearing degree of the paint while running the tire under a loaded condition. With such a method, when the paint is worn due to a pressure contact with the road surface during the running of the tire under a loaded condition, the wear amount of the regularly coated paint increases due to slips and resultant friction force occurring on the surface of the respective ridge portions of the tire. This makes it possible to accurately estimate the irregular wear state of the tread surface, by visual observation and inspection of the wear state of the paint.
The wearing state estimating method disclosed in JP-A-8-29296 requires setting of a relatively large distance between the coated paint dots so that the tread surface is significantly exposed and the friction characteristic of the tread rubber is more accurately reflected to the wear amount of the paint, with a premise that the irregular wear of the entire tread surface is estimated solely by the wear information of the painted portion. Accordingly, it may be difficult to achieve a satisfactory accuracy of estimation of irregular wear of tires. The known method is capable of estimating irregular wear only by two kinds of information obtained before and after the running of the tire under the loaded condition. This means that the progress of wearing degree cannot be grasped in a time sequence. In such a context, it may be difficult to further improve the accuracy of estimation.